Motor-control system



Nov. 11 1924. 1,515,215

G. E. KING MOTOR CONTROL SYSTEM Filed Feb. 8. 192's WITNESSESZ INVENTOR- v Gecg; e E. King.

' ATTORNEY Patented Nov. 11, 1924.

UNITED STATES PATENT OFFICE.

GEORGE E. KING, OF WILKINSBURG. PENNSYLVANIA, ASSIGNOR TO. WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

MOTOR-CONTROL SYSTEM.

Appflication filed February 8, 1923.

To all whom it may concern:

Be it known that I, GEORGE E. KING, a citizen of the United States, and a resident of Wilkinsburg, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Motor-Control Systems, of which the following is a specification. I

My invention relates to motor-control systems and it has particular relation to such systems as employ means for the protection and for controlling the speed of electric motors.

One object of my invention is to protect motors and apparatus operated thereby against damage in the event of failure of Another object is toprovide manual and automatic means for adjusting the motor operatin speeds.

Accor ing to my system, I preferably emplo an adjustable-speed shunt-wound motor wit a manually operable field rheostat for adjusting the motor speed, and additional means for modifying the effect of the field rheostat. In addition, I provide an automatically controlled device that becomes operative, in the event that load is temporarily removed and later restored, to protect the motor against objectionable surges of current.

My invention will be described in connection with the accompanying drawing, in which the single figure is a diagrammatic view of circuits and apparatus embodying my invention.

A motor having an armature 1 and series and shunt field-magnet windings 2 and 3, respectively, is operatively connected, through a line switch 4, to line conductors 5 and 6. An accelerating resistor 7 is provided for connection in the armature circuit and is controlled by accelerating switches 8 and 9. An interlock 11 is mechanically attached to, and operated with, switch 4. A rheostat 12 is connected in circuit with shunt field winding 3.

A field relay 13, having an operating coil 14, is controlled by means of a pair of fast and slow push-button switches 15 and 16 that are mechanically interlocked and pivotally mounted on a lever 17. Customary ,start and stop buttons 18 and 19,

are provided for controlling respectively,

and a relay 21,hav1ng a shunt line switch 4,

Serial No. 617,734.

operating coil 22 and a series holding coil 23, is preferably provided for controlling accelerating switches 8 and 9. The motor may be connected for driving a load, and my invention is of particular value for operating machines requiring low starting torque and a rapidly increasing torque characteristic, upon increase of speed, such as is the case with a fan or a pump.

Assuming the apparatus to be in its illustrated inoperative condition, the rheostat 12 may be first adjusted for any desired running speed. The motor is started by momentarily depressing button 18 to close line switch 4. A circuit is thereupon established from line conductor 5 through push-button 18, stop button 19, operating coil 24, con-,

ductor 25 and series coil 23 of relay 21 to line conductor 6. Upon the closure of line switch 4, the armature 1, field-1nagnet winding 2 and resistor 7 are connected to line conductors 5 and 6, respectively. Operating coil 14 of relay 13 is connected to line conductors 5 and 6 through line switch 4 and push-button 15; the relay, therefore, closes to shunt rheostat 12. Shunt field-magnet winding 3 is now directly connected to line conductors 5 and 6 through line switch 4 and relay 13.

Shunt coil 22 of relay 21 is connected to the terminals of resistor 7, and, therefore, is energized in accordance with the voltage across resistor 7. Relay 21 is closed immediately after the closure of line switch 4. As the armature 1 is accelerated, resistor 7 is gradually shunted by switches 8 and 9, which may be controlled in any known manner, as, for example, in accordance with the increasing counter-electromotive force of armature 1. Operating coils 26 and 27 are connected in shunt relation to armature 1 through interlock 11 and relay 21. \Vhen accelerating switches 8 and 9 are closed, the motor operates at its normal speed, with maximum field excitation. Coil 22 of relay 21, being subject to the voltage across resistor 7, is now de-energi'zed, but relay 21 is maintained closed by means of coil 23, which is effective as long as appreciable current traverses the motor armature 1.

If, for any reason, load is temporarily removed from the motor, the armature current is naturally reduced to its no-load value, series coil 23 is consequently dc-energized, and relay 21 opens to interrupt a circuit through coils 24, 26 and 27 of switches 4, 8 and 9. Switches 4, 8 and 9 then open to stop the motor and to protect apparatus driven thereby from possible injury.

By depressing the fast button 15, the operating coil 14 of relay 13 is transferred fro a line-energized circuit previously traced to a circuit in shunt relation to resistor 7. Relay 13, therefore, remains closed only during the starting period, in accordanoewith the drop in potential across resistor 7. Under these conditions, the motor will continue to accelerate, upon the opening of relay 13, to a speed corresponding to the adjustment of rheostat 12. The motor speed may now be regulated by manipulating rheostat 12. When it is desired to suddenly reduce the speed to a value corresponding to maximum field excitation, the operator may push the slow button 16, whereupon relay 13 again closes to shunt rheostat 12, the operating coil 14 being again connected to line conductors 5 and 6. When it is desired to again operate the motor at exactly its former predetermined speed, fast button 15 is again operated to open relay 13, and the motor rapidly accelerates to its former speed value. In this way, the motor speed may be changed rapidly from minimum to maximum without the necessity 'formanipulating rheostat 12.

For speed control in accordance with my invention, there are a number of desirable methods of operation, such as first operating the slow button and then the start button, whereupon the motor accelerates to its will accelerate to a speed corresponding to the setting of the field rheostat. The field rheostat may then bemanipulatedto attain any desired operating speed. Upon actuating the slow button, the motor is immediately slowed down and may be thereafter immediately returned to its previous operating speed, upon the actuation of the fast button, without disturbing the setting of the field rheos at.

These features of s eed control, together with the protection a orded against damage to the motor or apparatus driven thereby upon failure of load, will be recognized as desirable in many motor applications.

I claim as my invention: 1. The combination with a motor and a starting resistor therefor, of voltage conti'olled means for shunting the resistor during starting and means for restoring said shunting means upon failure of load.

2. The. combination with a motor and a starting. resistor therefor, of means for shunting the resistor during starting, means dependent upon current traversing said resistor for controlling the shunting means, and

means for thereafter controlling said shuntingdl means in accordance with the motor 0a r Y 3. The combination with a motor and a starting resistor therefor, of means for. shunting the resistor, a line switch, and a relay for controlling the shunting means and the line switch, having coils connected respectively in shunt and in series relation with respect .to said resistor.

4. The combination with a motor having a shunt field-magriet winding and means for regulating the effect of said winding, of means for insuring maximum field strength during starting, and means for controlling the effect of said regulating means during normal operation of the motor.

5. The combination with a motor having an armature and a shunt field-magnet winding, of a rheostat for controlling said winding, means for automatically shunting the rheostat during starting, and means for 'controlling said shunting means during normal operation of the motor.

6. The combination with a motor having an armature and a shunt field-magnet winding, of a rheostat for controlling said winds ing, a relay having a coil subject to armature current during starting for shunting the rheostat, and means for rendering said coil subject to impressed motor voltage during normal running of the motor.

7. The combination with a motor having an armature and a shunt field-magngt winding, of a rheostat for controlling said winding, and means for shunting the rheostat comprising a coil selectively controlled by impressed motor voltage or by armature current.

8. The combination with a motor having a shunt field-magnet winding and regulating meanstherefor, of a starting resistor, means controlled in accordance with current traversing said resistor for controlling said regulating means, and means for controlling the second named means during normal operation of the motor.

9. The combination with a motor having a shunt field-magnet Winding and regulating means therefor, of a starting resistor, means controlled in accordance with current traversing said resistor for controlling said regulating means, and means dependent upon thefvalue of current required by the motor during normal operation for controlling the second named means.

10. The combination with a motor having a shunt field-magnet winding and regulating means therefor, of a starting resistor, means controlled in accordance wi h current traversing said resistor for controlling ing, of a starting resistor, a field rheostat for regulating the motor speed, a relay having a coil arranged, selectively, for separate excitation or for connection in shunt relation to the starting resistor, manual means for controlling said relay connections for controlling the effect of said rheostat, and means dependent upon the value of current traversing the armature for controlling said starting resistor.

In testimony whereof, I have hereunto subscribed my name this first day of February 1923. 1

GEORGE E. KING. 

